Considering that the RIS is often installed at the facade of tall buildings and the BS also have a certain height, as in [1]}, [2]}, [3]}, we adopt Rician fading to model the RIS-related channels as
\(\begin{array}{l}\mathbf {h}_{k}\!=\!\sqrt{\frac{\alpha _{k}}{\varepsilon _{k}+1}}\left(\sqrt{\varepsilon _{k}} \,\overline{\mathbf {h}}_{k}+\tilde{\mathbf {h}}_{k}\right),\mathbf {H}_{2}=\sqrt{\frac{\beta }{\delta +1}}\left(\sqrt{\delta } \, \overline{\mathbf {H}}_{2}+\tilde{\mathbf {H}}_{2}\right),\end{array}\) 
